Apparatus for producing iron alloy powder



Aug. 7, 1945. J. WULFF 2,381,023

APPARATUS FOR PRODUCING IRON ALLOY POWDERS Filed June 4, 1940 B F :2; iI

\ 1- FURNACE 1,

;;U LADLE 1'0 LADLE CERAMIC SCREEN pi) a ::1 WATER JET WATER QUENCH TANKSTAMP MILL BALL MILL 7 M SCREEN 6 L A ,*\-Mns-znc SEPARATOR 9 cnRazozP)OWDER sum- 10 -E nzcnnsumzma CEMENTITE RICH D ACE) POWDER DEcARsumzmaj Hz FURNACE IRON POWDER OR IRON ALLOY POWDER grvue/who a Patented Aug.7, 1945 UNITED STATES PATENT oFFlcE APPARATUS FOR PRODUCING IRON ALLOYPOWDER John Wolff, Cambridge, Mass.

Application June 4, 1940, Serial No. 338,827

10 Slaims.

sion and heating or sintering the compact.

-The potential field of use of metal powders for the production ofcompacts is very wide, however, the immediate extension is'hampered in anumber of particulars. As a general proposition, where only strictlymechanical factors are involved in the use of a machine element, apowder metal compact can compete with machined products, produced byfusion metallurgy, only when the machining operations are relativelycostly, This is due to the fact that" a machine element made up of apowder compact, per unit of weight, is considerably more expensive thanwhen produced by conventional methods from the liquid phase metal. Theextension of powder metallurgy is particularly limited in those useswhere alloy steels of special specifications are required.

It has been suggested heretofore to produce metal compacts byforming thecompact in the desired element shape from iron powder and modifying thephysical characteristics of the surface, such for example as increasingthe hardness by carburizing or case hardening the surface. It has alsobeen suggested to produce fabricated units of alloy steels, by powdermetallurgy methods, by mixing predetermined percentages of iron powderand a powder of t a l y I gredients. These products are expensive due toa high initial cost of the iron powder as well as the alloy additionagents. a

The present invention deals with the concept of extending the field ofuse of ferrous powder metallurgy by providing a simple and efficientapparatus in which cheaper forms of ferrous materials may be processedto produce efficient iron and iron alloy powders.

The present invention relates to the subject matter disclosed in myapplications Serial Nos. 338,825 and 338,826, filed June 4, 1940.

As explained in the earlier applications, the novel apparatus describedherein is developed for the purpose of utilizing a very cheap source ofiron such as relatively high carbon pig iron or alloy steel scrap,melting this down in eflicient furnace equipment and subsequentlyprocessing this melt to produce iron powder or iron alloy powders ofpredetermined carbon analysis. As described in the cross referencedapplications, in the new method a high carbon iron or iron alloy melt israpidly quenched so as to produce in effect a white cast iron, i. e., avery brittle structure low in austenite and high in brittleconstituents, such as cementite, pearlite and martensite. The

apparatus described herein is designed so as posi-,

tively to achieve a desirable brittleness. After production of the solidphase brittle cast iron, means are provided to disintegrate the materialand subsequently to separate the material into fractions" relativelyrich and relatively poor in carbon. Depending upon the particularspeciflcations, especially with respect to carbon, which are required,the low carbon fraction is further processed to reduce the carboncontent and addition-alloy to advantageously modify the physicalcharacteristics so as to render the ultimate powder more amenable tocompacting and sintermg.

In order to more fully explain the invention a preferred apparatus isshown in diagrammatic form in the accompanying drawing, in which Fig. 1is a flow sheet of the apparatus and Fig. 2 is a diagrammaticillustration of an electric furnace which may be employed in theapparatus.

In carrying out the process cheap raw material, such as a cheap pig ironlow in phosphorous,

sulphur and silicon, is charged to a suitable furnace I. This fur'nacemay be of any suitable type, such as an electric furnace as shown inFig. 2 or an efiicient type of cupola furnace as shown in Fig. 1. Whenhigh iron alloys, such as the high chromium alloy powders, are to bepro-7 duced any suitable type of electric furnace may be employed. Whenproducing iron alloy powders, and depending upon the particular ultimateiron alloy powder desired, alloy addition agents, such as chromium,vanadium, molybdenum, manganese, tungsten and the like may be added tothe melt either in the form of pure metals, ferro alloys or alloy scrap.*When utilizing alloy steel scrap as the sole charge, such scrap may bemelted down in an electric furnace under a car- 'bon blanket so as toinsure a high carbon content in the melt and a consequent brittleness inthe quenched material.

The charge in cupqla furnace l or electric ceramic. The screen serves todivide the mass of molten metal into a series of streamlets and theseare immediately quenched and shotted by means of water or other suitablequenching medium forced through the appropriately positioned jets 4.This quenching and shotting serves to divide the cast metal into shot ofthe order of about 1; to /4 of an inch or finer. The shotted material isdischarged into a water container 5.

The material thus produced is essentially a white cast iron or alloycast iron and because of its high percentage of cementite ischaracterized by an extreme brittleness. If the silicon and othergraphitizing agents are kept low in the melt there will be a minimum offree graphite or temper carbon and the shot material will be extremelyhard. This brittleness is advisedly sought and employed for the purposeof disintegrating the shot in standard equipment and subdividing thematerial into a carbon rich fraction and an iron or iron alloy richfraction relatively low in carbon. For this purpose the shotted materialmay be taken either from storage or directly from the container 5 andpassed to any suitable type of stamp mill 6. If desired the materialdischarged from the stamp mill may be classified and the largerparticles returned for further disintegration. After reduction in thestamp mill to an intermediate degree the product is charged to a ballmill I and there further reduced in size. The brittle cementite willcrush very readily and also assist in crushing the more metallicpearlite, martensite; troosite or undecomposed austenite which may bepresent. The disintegrated product is discharged from the ball mill tothe screen 8 and-a fine powder of from 100 to 200 mesh or more averagesize is conveyed to the magnetic separator 8. The larger particles discrged from screen 8 may bereturned to the ball mill for furtherreduction. The material discharged from ,the ball mill which is finerthan 100 mesh will be comprised of substantially 75% cementite.

The brittle powder, separated out magnetically in the separator 8 may becharged to any suitable decarburizing furnace III. This powder may bedecarburized, as is known, at a temperature of from 400 to 800 C. in anatmosphere of a re non-magnetic tailing. In this way a cementite richpowder may be produced.

It will be appreciated that in this type of apparatus a plurality ofuseful products may be produced. The fine iron or iron alloy powder oflow carbon content, obtained from the decarburizing furnace l0, may bediluted and homogeneously admixed with the carbon rich fines, obtainedin separator 9 to produce a compact of the desired carbon analysis. Thecarbide powder separated'out in magnetic separator 9 may be used eitherdirectly or after any predetermined treatment as an abrasive or metalcleaning compound. Similarly, this carbon rich powder may, if desired,be admixed with pure iron powder for making powder compacts of aspecified carbon content Or it may be mixed with tungsten and iron,tungsten and cobalt, tlmgsten and vansdium and the like to produceimproved metal carbide containing tools which closely approximate thecomposition of the high speed tools.

As explained in copending application Serial No. 338,825, in producingcompacts from the improved iron powders or iron alloy and/or carbidepowders, established powder metallurgy methods may be employed. In theevent that the flow factor of the powder which is employed is below thatwhich is desired this may be improved by coating the powder with stearicacidor similar particular units described.

ducing gas such as hydrogen, hydrogen-steamer other decarburizing agentso as to reduce the carbon content to the desired degree. With such atreatment the 'pearlitic powder may be reduced from a carbon content ofthe order of 1.7% to -8% or lower. This decarburization treatment atelevated temperatures also beneficially modifies the powder for ultimateuse in powder compacts so that it is sufficiently plastic under pressureto make dense compacts. During this decarburization' treatment, as thoseskilled in the art will appreciate, the pearlitic surfaces of theparticles are decomposed to form the softer more plastic ferrite; Bycontrolling the temperatureand time of this treatment the depth of thisferritic case may be controlled. The product produced is new in thefield of powder metallurgy and is particularly useful for compacting,comprising as it does a tough core having an integral more plasticsurface or case.

when desirable, and prior to treatment in the decarburising furnace ill,the magnetic concentrate obtained from the magnetic separator 9 mayagain be milled so as to establish an optimumsize distribution and maythen be passed through the magnetic separatorto separate a relativelymagnetic concentrate from a-relatively I claim:

1. An apparatus for producing iron powder and iron alloy powder forpowder metallurgy comprising a furnace, a quenching means associatedwith the furnace Ito quench and shot a furnace heat, means todisintegrate the shotted material and a magnetic separator adapted toseparate the disintegrated material into a carbon-poor powderconcentrate and a carbon-rich powder tailing.

2. An apparatus for producing iron powder and iron alloy powder forpowder metallurgy comprising a furnace, a quenching means sssociatedwiththe furnace and adapted to quench and shot a furnace heat,- meansrtodisintegrate the shotted material, means to classify the disintegratedProduct and means to separate the product into a relatively magnetic anda relatively non-magnetic fraction of different carbon analysis.

3. An apparatus for producing iron powder and iron alloy powder forpowder metallurgywhich comprises a furnace, a quenching meansassociaied'with the furnace and adapted to quench a furnace heat,mechanical means to disintegrate the quenched material, means toseparate the material into a carbon rich and a carbon-poor 'frac-' tionandmeans to decarburize the carbon-poor fraction. A a

-'4. An apparatus for producing iron powder and mined fineness, magneticmeans to separate the material into a carbon-rich and a carbon-poorfraction and means separately to decarburize the fractions.

5. An apparatus for producing iron powderand iron alloy powders forpowder metallurgy which comprises a furnace, means associated with thefurnace to quench and shot a furnace heat, a stamp mill adapted todisintegrate the shotted material a magnetic separator associated withthe stampmill and adapted to separate the disinte grated material into arelatively magnetic concentrate and a relatively non-magnetic tailing.

6. An apparatus for producing iron powder and,

iron alloy powder for powder metallurgy which comprises a furnace, meahsassociated with the furnace to quench and shot a furnace heat, a stampmill, means tofeed the shotted material to the the mill, a ball milladapted to receive and further disintegrate the product from the stampmill, means to screen the product from the ball mill and means toseparate the screened product into carbon-rich and carbon-poorfractions.

7. An apparatus for producing iron alloy powder for powder metallurgywhich comprises an electric furnace, a quenching means associated withthe furnace and adapted to quench and shot an alloy heat, mechanicalmeans to disintegrate the shotted material and means to separate thedisintegrated product in carbon-rich and carbonpoor fractions.

8. An apparatus for producing iron alloy powder for powder metallurgywhich comprises an electric furnace, a quenching means associated withthe furnace and adapted to quench and shot an alloy heat, mechanicalmeans to disintegrate the shotted material, means to separate thedisintegrated product in carbon-rich and carbonpoor fractions and meansto decarburize the carbon-poor fractions.

9. An apparatus for producing iron powder for powder metallurgycomprising a cupola furnace, a quenchin means associated with thefurnace and adapted to quench and shots. highcarbon iron heat,mechanical means to disintegrate the shotted material and magnetic meansto separate the disintegrated product into carbon-rich JOHN WU'LFF.

